How do I have two different 'template_icon_view's in a panel?
I just made everything double:

import os
import bpy


def enum_previews_from_directory_items(self, context):
    """EnumProperty callback"""
    enum_items = []

    if context is None:
        return enum_items

    wm = context.window_manager
    directory = wm.my_previews_dir

    # Get the preview collection (defined in register func).
    pcoll = preview_collections["main"]

    if directory == pcoll.my_previews_dir:
        return pcoll.my_previews

    print("Scanning directory: %s" % directory)
    def_dir = os.path.dirname(bpy.data.filepath) + directory[1:]
    if directory and os.path.exists(def_dir):
        # Scan the directory for png files
        image_paths = []
        for fn in os.listdir(def_dir):
            if fn.lower().endswith(".png"):
                image_paths.append(fn)
        for i, name in enumerate(image_paths):
            # generates a thumbnail preview for a file.
            filepath = os.path.join(def_dir, name)
            thumb = pcoll.load(filepath, filepath, 'IMAGE')
            enum_items.append((name, name, "", thumb.icon_id, i))

    pcoll.my_previews = enum_items
    pcoll.my_previews_dir = directory
    return pcoll.my_previews

def enum_previews_from_directory_items2(self, context):
    """EnumProperty callback"""
    enum_items = []

    if context is None:
        return enum_items

    wm = context.window_manager
    directory = wm.my_previews_dir2

    # Get the preview collection (defined in register func).
    pcoll = preview_collections["main2"]

    if directory == pcoll.my_previews_dir2:
        return pcoll.my_previews2

    print("Scanning directory: %s" % directory)
    def_dir = os.path.dirname(bpy.data.filepath) + directory[1:]
    if directory and os.path.exists(def_dir):
        # Scan the directory for png files
        image_paths = []
        for fn in os.listdir(def_dir):
            if fn.lower().endswith(".png"):
                image_paths.append(fn)
        for i, name in enumerate(image_paths):
            # generates a thumbnail preview for a file.
            filepath = os.path.join(def_dir, name)
            thumb = pcoll.load(filepath, filepath, 'IMAGE')
            enum_items.append((name, name, "", thumb.icon_id, i))

    pcoll.my_previews2 = enum_items
    pcoll.my_previews_dir2 = directory
    return pcoll.my_previews2

class PreviewsExamplePanel(bpy.types.Panel):
    """Creates a Panel in the Object properties window"""
    bl_label = "Previews Example Panel"
    bl_idname = "OBJECT_PT_previews"
    bl_space_type = 'PROPERTIES'
    bl_region_type = 'WINDOW'
    bl_context = "object"

    def draw(self, context):
        layout = self.layout
        wm = context.window_manager

        row = layout.row()
        row.prop(wm, "my_previews_dir")

        row = layout.row()
        row.template_icon_view(wm, "my_previews")

        row = layout.row()
        row.prop(wm, "my_previews")

        row = layout.row()
        row.prop(wm, "my_previews_dir2")

        row = layout.row()
        row.template_icon_view(wm, "my_previews2")

        row = layout.row()
        row.prop(wm, "my_previews2")


# We can store multiple preview collections here,
# however in this example we only store "main"
preview_collections = {}


def register():
    from bpy.types import WindowManager
    from bpy.props import (
            StringProperty,
            EnumProperty,
            )

    WindowManager.my_previews_dir = StringProperty(
            name="Folder Path",
            subtype='DIR_PATH',
            default=""
            )

    WindowManager.my_previews = EnumProperty(
            items=enum_previews_from_directory_items,
            )
    WindowManager.my_previews_dir2 = StringProperty(
            name="Folder Path",
            subtype='DIR_PATH',
            default=""
            )

    WindowManager.my_previews2 = EnumProperty(
            items=enum_previews_from_directory_items2,
            )

    # Note that preview collections returned by bpy.utils.previews
    # are regular Python objects - you can use them to store custom data.
    #
    # This is especially useful here, since:
    # - It avoids us regenerating the whole enum over and over.
    # - It can store enum_items' strings
    #   (remember you have to keep those strings somewhere in py,
    #   else they get freed and Blender references invalid memory!).
    import bpy.utils.previews
    pcoll = bpy.utils.previews.new()
    pcoll.my_previews_dir = ""
    pcoll.my_previews = ()
    pcoll2 = bpy.utils.previews.new()
    pcoll2.my_previews_dir2 = ""
    pcoll2.my_previews2 = ()

    preview_collections["main"] = pcoll
    preview_collections["main2"] = pcoll2

    bpy.utils.register_class(PreviewsExamplePanel)


def unregister():
    from bpy.types import WindowManager

    del WindowManager.my_previews

    for pcoll in preview_collections.values():
        bpy.utils.previews.remove(pcoll)
    preview_collections.clear()

    bpy.utils.unregister_class(PreviewsExamplePanel)


if __name__ == "__main__":
    register()


I am sure It can be done more professionally, but it's good starting point.
If You want more than two You should reed about collections